DENVER — Disney is opening its Broadway-bound “Frozen” Thursday night to a sea of Elsas.

Easily one-third of the audience for the last month of previews has arrived in long blue gowns and blond wigs with braided ponytails. Most are young girls, to be sure, but Elsa touches all ages. Grown women show up wearing ice-princess crowns, and Tuesday night, an entire family came in costume: Dad wore a full-on Olaf snowman suit, Mom had on the long blue gown, their daughter sported Princess Anna mountaineering gear and their son wore Kristoff’s fur cap.

If they’d brought their dog, it would probably have come as Sven, the reindeer.

Kristoff (Jelani Alladin) and Sven (Andrew Pirozzi)Deen van Meer

One night, a boy wearing an Olaf hat sat dead center in the first row. Every time the actors looked down at the orchestra, they saw a carrot nose sticking up from behind the conductor’s head.

“Frozen” is the most successful animated movie of all time, and Disney’s challenge has been to preserve beloved moments from the film while expanding the story and deepening the characters to fill out two hours or so of stage time.

Judging from the reaction of audiences here, Disney’s on the right track.

“I love the movie, but the musical’s a lot better,” says 11-year-old Paige Rosener. “It has much more feeling.”

Directed by Michael Grandage and designed by Christopher Oram, the production — which opens at Broadway’s St. James Theatre in February — features sumptuous sets, gorgeous costumes and plenty of special effects to wow the boys in the audience. Disney never discloses costs, but estimates range between $30 million and $40 million.

‘I love the movie, but the musical’s a lot better. It has much more feeling.’

Young Elsa and Anna sleep in enormous canopied beds in the vast royal castle at Arendelle. After Elsa injures Anna with her powers, she seals herself off from the world behind two monstrously large castle doors. Her palace engulfs the stage in glittering crystal chandeliers and icicles that stretch to the heavens. When Anna searches for Elsa in the mountains, she and Kristoff cross an ice bridge that spans the length of the stage.

“I really love the ice bridge,” says Patti Murin, who plays Anna. “It took us a while to figure it out, double-checking to make sure we’re hooked in so we don’t die up there. But now we’ve got it down, so we can just enjoy the scene.”

While dangling from the bridge, Anna and Kristoff (played by the winning Jelani Alladin) sing “What Do You Know about Love?” one of several new songs by the husband-and-wife team of Kristen Anderson-Lopez and Robert Lopez.

Alladin as Kristoff and Patti Murin as Anna “Frozen: The Musical.”Deen van Meer

Another new song, “Monster,” is a walloping 11 o’clock number for Elsa. As the villagers hunt her down with pitchforks, she stands alone in her castle singing about what it’s like to be misunderstood, to be seen as a monster when you’re really just a frightened young woman.

“There’s a big turning point for the character in that song,” says Caissie Levy, who plays Elsa. “I love the reaction we get when the songs come that the audience knows. But the real fun is watching them take in the new material. That’s when they go ballistic.”

Of course, you don’t mess with what works, so all the famous songs from the movie are in the musical. You’ve probably heard “Let It Go” once or twice or, if you’re a parent, a thousand times, but it brings down the house at the end of Act 1.

The moment the orchestra strikes up the first familiar notes, girls all over the theater stand up, reach out to Elsa, mimic her hand movements, and warble, “The cold never bothered me anyway.”

Olaf, a life-size snowman puppet who looks the same as he does in the movie, has his nifty little vaudeville number that’s set on the beach. Actor Greg Hildreth plays him with aplomb.

Murin plays Anna with all the wit and spunk of a young Julie Andrews in “The Sound of Music.”

Michael Curry, who worked with Julie Taymor to create the astonishing puppetry in “The Lion King,” designed the puppets for “Frozen.” He’s outdone himself with Sven, Kristoff’s reindeer companion.

Andrew Pirozzi plays Sven, and though he never says a word — or takes off his reindeer headdress — this guy deserves a Tony nomination. He walks on all fours throughout the show and operates Sven’s twitching ears and blinking eyes. There’s so much feeling and emotion in those eyes that you forget it’s just a puppet.

“Mommy,” a little boy was overheard asking, “can I pet Sven?”

One major departure from the movie was eliminating the boulders that become trolls.

“I just couldn’t see that,” Grandage tells The Post. “We’re going to have rocks gathering moss on stage? No, no.”

Instead, Grandage introduced the Hidden Folk. Inspired by hulders, seductive forest creatures from Scandinavian folklore, they’re part human, part animal (they have tails). As played by beefy chorus boys and sexy chorines, these hulders are hotties.

For all its lavishness, the story is basically an intimate one about two sisters. Disney could spend a billion dollars on the production, but if Elsa and Anna had no chemistry, “Frozen” would never melt your heart.

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And here Disney’s struck gold. Murin plays Anna with all the wit and spunk of a young Julie Andrews in “The Sound of Music.” Levy brings an elegance and remoteness to Elsa that recalls Meryl Streep’s in “The French Lieutenant’s Woman.”

Murin’s been with the show from the first reading, but Disney couldn’t offer her the part until she was paired with the right Elsa.

“I needed someone who could act the role, which is difficult, who’s beautiful and on top of that is a belter,” Grandage says. “Usually you have to prioritize. Caissie came in with it all.”

Levy and Murin have developed a huge fan base here in Denver. Packs of little Elsas and Annas wait for them at the stage door every night.
“Their moms and dads have to say, ‘There’s Elsa and Anna!’ because we’re in our street clothes,” says Levy.